DESCRIPTION: The long-term objectives of this application are to gain a better understanding of the mechanisms of dental caries and to provide rational bases for improved preventive of therapeutic regimens. The applicant proposes to conduct basic studies of the demineralization kinetics of carbonated apatites (CAP's) and human dental enamel (HE) with a general objective of establishing how demineralization depends on the composition of both the mineral phase and the external dissolution medium. In particular, the concept of metastable equilibrium solubilities (MES) will be used to study CAP and HE under a variety of synthesis conditions and solution conditions. Temperature pretreatment will also be used as a probe, which, together with mineral phase variables, should provide both fundamental information on structural order and solubility changes. This information may suggest possible mechanisms by which laser irradiation might act in reducing the susceptibility of human enamel to acid attack. The applicant has shown that CAP and HE have a distribution of apparent solubilities (MES). MES distributions have been shown to govern both initial dissolution rates and metastable equilibrium for up to 8 days. The dissolution driving force is governed by a surface complex that does not involve carbonate, although the magnitude of the driving force depends on the internal carbonate content of the mineral and its related crystallinity. The specific aims are 1) to examine the range of applicability of the MES and of the surface complex hypothesis with emphasis on employing composition and crystallinity of the CAP preparations as the independent variables; and 2) to test the hypothesis that temperature treatments in the range of 200-500 C of HE and CAP can cause abrupt changes in structural order, resulting in abrupt changes in solubility (MES) and that these effects are dependent on crystallinity and/or carbonate content. Assessment methods including chemical analysis, IR spectroscopy, X-ray diffraction, BET surface analysis, transmission electron microscopy (TEM), MES determinations, and initial dissolution rate determinations will be utilized. As the study progresses, information will be brought together to provide a basic rationale for the behavior of CAP, HE and perhaps in the broader sense, human dentin or bone mineral.